236 
CHARADRIIFORMES 
# 
Distribution. A bird of the prairie interior, probably nesting in any suitable place 
wherever found in Canada. Not yet reported from British Columbia, although there are 
records from the State of Washington. There are old records for southern Ontario, but 
not from farther east. 
These terns frequent marshes rather than beaches and do not seem 
to gather in such large flocks on the big lakes as do the Common Tern, to 
which they are otherwise very similar in habit. Though common through- 
out the eastern prairie sections they are more local and less generally 
distributed than the Common Tern. 
70. Common Tern. Wilson’s tern, la sterne commune. Sterna hirundo, L, 
15 (Forking of tail 3-1). Plate XXIX A. 
Distinctions. East, central, and west. The Common Tern resembles both the Arctic 
and Forster’s Terns so nearly as to require close attention to small details to separate it 
from them. The certain characteristic by 
which it can be separated from Forster’s, 
but not the Arctic, is the coloration of 
the long outer tail feathers, which are 
shaded with dark on the outer instead of 
the inner web (Figure 347). The under- 
parts in the adult are also delicately 
shaded with pearly grey, averaging 
appreciably lighter than the Arctic but 
slightly darker than Forster’s. This dis- 
tinction does not always hold with juvenile 
birds. In young or autumn plumages, 
the face markings are quite distinct from 
those of Forster’s, but not from the Arctic. 
In the Common Tern, the dark face patch 
suffuses across the nape of the neck to 
meet its fellow from the opposite side, 
making a continuous nape band (Com- 
pare with Figure 346). In juvenility the 
bill is largely flesh coloured and black 
and in the autumn adult much of the 
redness is lost. From the Arctic Tern distinction is rather more difficult. The grey below 
does not average quite as deep, but this characteristic is not common to all individuals. 
The forward third of bill of the adult Common Tern is black, but the bill of the Arctic is 
red to the tip. The only distinction from that species that holds in all plumages is that 
of the feet and legs. Those of the Arctic Tern are particularly small, the tarsus being not 
more than 0-65 inch in length; that of the Common Tern is not less than 0-8 inch. 
Field Marks. In mixed flocks of Common and Forster’s Terns the Common can some- 
times be distinguished by the slightly greyish clouding of the white underparts. In autumn 
and juvenility it can be separated from Forster's by the face mark spreading over the back 
of the head. The best field distinction between the two species, however, is the call-note 
which is very different from that of Forster’s, which is a sharp “Tearrrr” instead of a duller 
and more woodeny-sounding “Churrir.” From the Arctic Tern differentiation is more 
difficult. The black-tipped instead of all red bill may be made out under favourable 
circumstances. When on the ground the Common Tern stands up higher on its legs than 
the Arctic Tern. The latter hugs the ground with its body as it walks, and has a mouse- 
like glide. The Common Tern is likely to be confused with Forster’s only in the interior, 
and with the Arctic only in the high north and on the two coasts. 
Nesting. On sandy or gravelly bars. Eggs laid directly on the ground. 
Distribution. Across the continent, breeding north to southern Labrador, .James 
Bay, and Great Slave Lake. This is the most abundant tern throughout most of southern 
Canada. 
Common, especially in the interior about sandy shores, scarcer on 
rocky ones. The Common Tern may be seen on most of our larger bodies 
of water, salt or fresh, throughout the summer. Its wonderful lightness of 
wing, and graceful circlings — one instant hovering on rapidly beating 
wings, stationary in the air, as it searches for some tid-bit below, and the 
next dropping like a plummet with a sparkling splash— are constant 
Figure 347 
Specific details of Common Tern; tail’and 
head of juvenile or w'inter plumage; 
scale, j. 
